1. Technical Field
The disclosure relates to light emitting diode lamps, and particularly to a control circuit for maintaining a luminous intensity of a light emitting diode lamp within an acceptable range in a long time.
2. Description of Related Art
Recently, light emitting diodes (LEDs) have become widely used in a variety of LED lamps, for example, miner's lamps, street lamps, submarine lamps and stage lamps, for their low power requirement and long lifetime. However, all LEDs present gradual luminous decay that is related to a driving current flowing therethough and a junction temperature thereof, and different LED designs present their own characteristic degradation rates.
With high-power LEDs, for example, in a high-power LED street lamp, along with an increased use time and a poor heat dissipation performance, a light output of the LEDs will gradually decrease due to the luminous decay, which is resulted in a luminous intensity of the LED street lamp greatly decreased. For road lighting, when the luminous decay is up to 30%, the lamps will not meet road illumination needs. That is, after a period of time, the LED street lamp cannot meet the lighting needs due to the luminous decay of the LEDs. The luminous decay of the LEDs results in a shortening of a life time of the LED street lamp below its actual serviceable time.
In order to obtain a longer life time, one way is to apply a larger driving current to the LED street lamp to drive the LEDs to emit light with a intensity higher than the rated, to thereby maintain a proper illumination of the LED street lamp even after a comparatively long period of time. However, the larger driving current through the LEDs causes excess of luminous flux output, which results in a waste of energy; on another aspect, this larger driving current accelerates luminous decay of the LEDs and causes damage to the LEDs.
It is thus desirable to provide an LED lamp with a control circuit which can overcome the described limitations.